Propagate workflow stderr to minimal log output

Changed stderr logging level from 2 to 0 so that error output
from workflows appears in the minimal log file, making it easier
for users to see errors without viewing full logs.

https://claude.ai/code/session_01L9vBwhCPsXUTTxen3sW8rn

Author: claude

src/workflow/CommandExecutor.py

@@ -153,7 +153,7 @@ def read_stderr():
             try:
                 for line in iter(process.stderr.readline, ''):
                     if line:
-                        self.logger.log(f"STDERR: {line.rstrip()}", 2)
+                        self.logger.log(f"STDERR: {line.rstrip()}", 0)
                     if process.poll() is not None:
                         break
             except Exception as e: